I believe this to be from a '68 Chevelle 396/350hp 4sp car (re. 'EF'), ...correct??Also, ...from what I've checked, ...it appears the heads are very late '68 heads??? (June 25th and July 10th) (ref. By the Numbers book, P. 103)

Correct with an addition that the engine could also have had a 3 speed manual transmission. The heads are listed as being used in 1969 applications with a note that they "could" have been used in 1968 engines built after June 25th, 1968, of which one of yours is that EXACT date!!